Monday, 13 July 2009

I’m a Firestarter, twisted firestarter

A flame is a mixture of reacting gases and solids emitting visible andinfraredlight, thefrequency spectrumof which depends on the chemical composition of the burning material and intermediate reaction products. In many cases, such as the burning oforganic matter, for example wood, or the incompletecombustionof gas,incandescentsolid particles calledsootproduce the familiar red-orange glow of 'fire'. This light has a continuous spectrum. Complete combustion of gas has a dim blue color due to the emission of single-wavelength radiation from various electron transitions in the excited molecules formed in the flame. Usually oxygen is involved, buthydrogenburning inchlorinealso produces a flame, producinghydrogen chloride(HCl). Other possible combinations producing flames, amongst many more, arefluorineandhydrogen, andhydrazineandnitrogen tetroxide.

The glow of a flame is complex.Black-body radiationis emitted from soot, gas, and fuel particles, though the soot particles are too small to behave like perfect blackbodies. There is alsophotonemission by de-excitedatomsandmoleculesin the gases. Much of the radiation is emitted in the visible andinfraredbands. The color depends on temperature for the black-body radiation, and on chemical makeup for theemission spectra. The dominant color in a flame changes with temperature. The photo of the forest fire is an excellent example of this variation. Near the ground, where most burning is occurring, the fire is white, the hottest color possible for organic material in general, or yellow. Above the yellow region, the color changes to orange, which is cooler, then red, which is cooler still. Above the red region, combustion no longer occurs, and the uncombusted carbon particles are visible as black smoke.

TheNational Aeronautics and Space Administration(NASA) of theUnited Stateshas recently found thatgravityplays a role. Modifying the gravity causes different flame types.[3]The common distribution of a flame under normal gravity conditions depends onconvection, as soot tends to rise to the top of a general flame, as in acandlein normal gravity conditions, making it yellow. Inmicro gravity or zero gravity, such as an environment inouter space, convection no longer occurs, and the flame becomes spherical, with a tendency to become more blue and more efficient (although it may go out if not moved steadily, as the CO2from combustion does not disperse as readily in micro gravity, and tends to smother the flame). There are several possible explanations for this difference, of which the most likely is that the temperature is evenly distributed enough that soot is not formed and complete combustion occurs.[4]Experiments by NASA reveal thatdiffusion flamesin micro gravity allow more soot to be completely oxidized after they are produced than diffusion flames on Earth, because of a series of mechanisms that behave differently in micro gravity when compared to normal gravity conditions.[5]These discoveries have potential applications inapplied scienceandindustry, especially concerningfuel efficiency.

In combustion engines, various steps are taken to eliminate a flame. The method depends mainly on whether the fuel is oil, wood, or a high-energy fuel such asjet fuel.

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